Electrolytic cell gas outlet



Oct. 15, 1940. E. R. CORNEIL ELECTROLYTIC CELL GAS OUTLET Filed om. 18, 1938 2 Sheets-Sheet 1 INVENTOR.

I ERNEST R. CORNEIL ATTORNEY;

Patented Oct. 15, 1940 PATENT OFFICE,

ELECTROLYTIC CELL GAS OUTLET Ernest R. Corneil, Niagara Falls, N. Y., assignor to E. 1. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Application October 18, 1938, Serial No. 235,626

10 Claims.

Thisinvention relates to an improvement in fused salt electrolysis cells, for example cells used to electrolyze metal halides to produce thecorresponding metal and halogen.

In the operation of the fused salt electrolysis cell, in the electrolysis of substances which evolve gaseous products at one or both electrodes, difliculty is ordinarily experienced because of more or less violent splashing of the molten salt electrolyte at the point where evolved gas leaves the.

o to solidify on such cooler surfaces and consequently it is necessary frequently to open the collecting device or gas lead-ofi-pipe and clean' out the solidified electrolyte. Sometimes this entails shutting down the electrolysis, which is 25 troublesome and expensive and even when it is not necessary to stop the electrolysis operation, opening the collecting device or pipes to clean out the frozen salt causes dilution of the gas with air, thereby resulting in a more impure gaseousproduct and escape of the gas, which is wasteful and often hazardous to the operator. 1

An object of the present invention is to prevent solidifying of the electrolyte in the gas collecting device of a fused salt electrolysis cell. A further object of the invention is to provide an improved apparatus for fused salt electrolysis in which gaseous products are formed. Other objects of the invention will be apparent from the following description thereof.

The above bjects of my invention are obtained by arrangement of a partition in a gas collecting device of usual design so as to form two adjacent chambers therein. The gas collecting device as usual is partially submerged in the electrolyte and arranged above the zone ofgas-ev0lution in the electrolytic cell and has a gas outlet in its non-submerged part. According to my invention said partition forming the two adjacent chamhers is positioned substantially in the submerged part of the gas collecting device and arranged in ,such a manner that one of the said chambers is open towards the zone of gas evolution and the other chamber is substantially separated from open towards the non-submerged part of the gas .after it has given oif t lre collecting device. Means are provided to allow the rising electrolyte to overflow from said first mentioned chamber into said other chamber gas suspended therein. This, for example, can beeffected by extending said partition to a point slightly below the level of said rising electrolyte in said first chamberor according'to my preferred way of carrying out my invention'by having perforations in said partition which in this case extends above the level of the electrolyte in said first chamber. By such an arrangement of perforations in said partition it is also obtained that 'thegas and the electrolyte are more completely separated in said first chamber. The perforations are preferably arranged in such away that they are positioned in the upper part of the partition extending approximately from its upper margin down to the level of lowest average fused'salt level in tfie cell outside of the gas collectingdevice. In the other chamber into which the electrolyte overflows from said first chamber suitable means are provided to recirculate the electrolyte back into the electrolyte in the cell preferably into a zone which is not subjected to the action of electric current.

Thus the gas collecting device of an electrolytic. cell may be divided by means of a suitable parti-' tion or bathe in such a manner that the diluent gases are directed from the bottom of the gas collecting device toward one side of the gas collecting device, thus providing a separate chamber. in thegas collecting device for the rising gases. The other chamber formed by said partition or baiile is arranged in such a way that the molten electrolyte rising with the gases will overflow into said chamber from said first chamber.

In the practice of my invention I preferably achieve this effect by arranging, for example in a gas collecting dome of a conventional type, an inclined baffle which divides the domeinto two adjacent chambers communicating at the upper part with each other, only the one chamber beingopenat its lower end toward the electrolysis cell. proper. Thus the effluent gases from said electrolysisprocess are collected at. one side of the dome and escape at the upper part of the. chamber into the gas collecting dome, while the fused salt rising with the gases overflows into the other chamber formed by said baflle. The

salt which has overflowed into said second chamber can be recirculated in any suitable manner into the electrolysis cell proper.

The baflie, dividing the gas collecting dome into two adjacent chambers communicating attheir upper parts with each other, is preferably perforated in its upper part so as to provide a large area for overflowing of the salt yand furthermore so as to separate thereby the bulk of the fused salt from the gases. It is also advantageous to arrange the bafile in such a way that the electrolyte overflows into the recirculation compartment through said perforations by extending the baflie substantially over the highest level attained by the electrolyte in the gas collecting compartment.

Although the function of this device is not exactly known it is believed that by concentrating the efiluent gases in a limited area by means of this arrangement of the baiile in the gas collecting device, the effluent gases thereby furnish sufficient heat to prevent freezing out of the electrolyte. In the gas collecting devices heretofore used, the gas was allowed to escape over a larger area and did not provide sufficient heat to prevent freezing out of the electrolyte in such a larger area. Moreover, by arrangement of perforations in the baffle, splashing of the electrolyte is restricted to a minimum, since the electrolyte circulates through the perforations while the gases substantially rise along the baflle into the nonsubmerged part of the gas collecting device, thus facilitating the separation of the gas in the electrolyte by the different directions of flow.

According to a preferred modification of my invention, the recirculation chamber of the gas collecting dome is arrangedin such a way that the fluid level in it is kept at a constant level, for example by means of an overflow pipe. Thus, the fluid level in the recirculation chamber is substantially independent of the fluid level in any other part of the electrolysis cell. As is known, the level of the fused salt in an electrolysis cell is different in different parts of the cell, and also varies throughout the operation of the cell. The level of the electrolyte in the cell decreases with consumption of the electrolyte, and is onlyreadjusted from time to time by the introduction of new raw material. The electrolyte in the gas collecting part of the electrolysis cell is always somewhat higher, due to the fact that the mixture of electrolyte and gases is specifically lighter than the pure electrolyte, and in addition thereto to the so-called gas lift effect of the ascending gases which tend to cause upward flow of the gases toward the point where the gas is discharged from the cell. Assuming, now, that the recirculation chamber of the gas collecting device were directly communicating with the electrolytic cell, the level of the recirculation chamber would be continuously changing, depending upon the changes in level in the cell proper; and moreover in any event would be substantially lower than in the gas collecting chamber. This, however, would cause the walls of the collecting device in the neighborhood of the upper level of the electrolyte in the gas collecting chamber to be appreciably cooler than the electrolyte, and thus lead to solidification of electrolyte in this part of the gas c01- lecting device. By keeping the level in the recirculation chamber constant according to my preferred form of carrying out my invention, the level in this chamber can readily be kept at a level not substantially lower than in the gas collecting chamber, and thus further assist in preventing solidification of the electrolyte.

By recirculating the electrolyte from the recirculation chamber bymeans of, e. g., an overflow pipe into the electrolysis cell proper, a further. advantage is obtained that a continuous circulation of the electrolyte throughout the cell is 01)- tained, thus providing thorough mixing of the electrolyte, and thereby increasing the efficiency 1 of the cell.

To illustrate my invention I will describe its adaptation to a well known type of fused salt 5 electrolysis cell, hereinafter referred to as the Downs cell, as it is described and claimed in U. S. P. 1,501,756. The Downs cell, as shown in the aforesaid patent, has a centrally located graphite anode surrounded by an annular steel 10 cathode, and is ordinarily used for the electrolysis of fused alkali metal halides to produce alkali metal and halogen gas, for example, to produce sodium and chlorine. Above the annular cathode is suspended a circular trough for collecting the 15 metal liberated at the cathode, while a coneshaped hood, surmounted by a cylindrical dome, is utilized to collect the product formed at the anode. In the normal operation of the Downs cell the rapid evolution of halogen gas causes 20 considerable splashing of the molten electrolyte in the dome at the top of the gas collector, which electrolyte tends to freeze onto the relatively cooler walls of said dome. To prevent blocking the off-gas pipe leading from the dome, it is necessary to remove frozen salt from the dome atfrequent intervals.

In adapting my invention to the Downs cell, I may insert therein the inclined battle, as illustrated by the drawings, or equivalent means to 30 prevent freezing out of the electrolyte. Fig. l is a diagrammatic'section of a drawing showing a Downs cell equipped according to the preferred modification of my invention. Fig. 2 is a sectional view of the gas collecting dome proper.

Fig. 3 is a horizontal sectional view of the gas collecting dome shown in Fig. 2 on plane AA of Fig. 2.

Referring to Fig. l, a Downs cell equipped according to my invention consists of an electrolyte 40 container which is lined with a suitable refractory material, a centrally located anode 2 made of graphite, an annular cathode 3 surrounding said anode, a cylindrical diaphragm 4 made of wire gauze and suspended between the anode and 40 the cathode, an inverted collecting trough 5 suspended above the cathode to collect rising alkali metal, and a conical gas collecting hood 6 surmounted by the gas collecting dome I having a gas outlet 8. The gas collecting hood Ii may be constructed of steel, since it is entirely submerged in the fused salt and is thereby protected from the action of the halogen gas. Gas collecting dome I may be constructed of nickel to withstand the action of halogen gas above the surface of the electrolyte. The alkali metal collector is provided with a pipe 9 through which molten alkali rises and is led into receiver Ill. The cell is provided with a cover H, in which there is an'opening l2 for feeding salt into the cell. I I may be omited if desired. The dome I is provided with an inclined baffle l3 having perforations M in its upper part and separating one part of the dome from the gas collecting hood 6. The

part of the dome separated from the gas collectthe perforations I being arranged in such a way 7 i The cover Correthat the lowest perforations are about level with the average level of the electrolyte in the electrolysis cell proper, so as to allow on shutting off of the electrolysis cell, the fused salt to be on equal levels in the different partitions. Without departing from the spirit of my invention, the baffle may be perforated over a, larger or smaller area, as desired. However, the arrangement of perforations in the lower part of the baffle might lead to the escape of gas into the recirculation chamber and thus to undesirable splashing in said chamber, whereas by limiting the area of the perforations to the top of the baffle only, the circulation would be restricted to an undesired degree and cause increased splashing in the gas collecting chamber. The recirculation chamber is connected to overflow pipe 16 by means of opening IS. The overflow pipe I6 has an overflow opening I! and a discharge hole 18 which in ordinary operation of the cell is usually closed and is only opened to drain out electrolyte when taking the cell apart for cleaning or repairing purposes.

In the operation of the above described device, the cell is operated in the usual manner. The gas evolved'at the anode rises upwardly in hood 6' and passes into'the dome I, directed in its flow by inclined b'afile l3. The rapid rise of the gas, as well as the light specific weight of the gaselectrolyte mixture, causes the liquid to rise in I the partition of the dome formed by the baflle forming the gas collecting chamber above the main level of the bath in the cell. The liquid overflows into the other'chamber through perforations l4, while the gases are released at the relatively limited opening of the gas collecting chamber. Some gas might also escape through perforations l4, but only in so small amounts that effective operation is not affected. From the recirculation chamber, the electrolyte flows through overflow pipe l6 and opening I! back into the electrolysis cell proper. In the operation of the cell shown in the figures the gases escape through a limited opening in the gas collecting chamber, so that the heat of the gases would be sufliciently high to prevent solidification of the electrolyte. Furthermore, the level of the electrolyte in the recirculation chamber is kept constant by means of overflow pipe l6, thus preventing undesirablechariges in temperature of the walls of the gas collecting'dome and assisting in preventing solidification of the electrolyte. The di rection of the flow of the electrolyte from the gas collecting hood upwards into the gas collecting chamber and from there through the recirculation chamber and overflow pipe l6 into the cell proper, not only prevents freezing out of the electrolyte at the point where the gas is discharged from the cell, but also provides for a continuous circulation of the electrolyte in a simple and effective way.

My invention is not restricted to a particular arrangement of the baille or of the recirculation and gas collecting chambers. Thus, for example,

1 inch from each other. Of course, the size and.

I the cell.

form of the perforations will be dependenton the thickness of the baille and the viscosity of the fused salt and the other conditions prevailing in Thus, for example, instead of circular perforations, perforations of any other shape such as slots or the like can be used.- However, in any case the perforations should be sufliciently small to prevent any considerable amounts. of gas to pass therethrough and usually perforations of a larger diameter than inch will not be suitable. Too small perforations,' on the other hand, will restrict the flow of electrolyte and be easily plugged and usually perforations substantially smaller than inch should not be used. However, my invention is not restricted to perforations of any specific shape or size, since any kind of perforations will bring about the desired effect to a certain degree and the above,

specific examples show only preferred embodiments of my invention which have been found suitable in practical application of my invention. Various othermodifications will be apparent to those skilled in the art. I

To those familiar with the construction and operation of fused salt electrolysis cells, it will be apparent that my invention is not restricted to the Downs type cell, and further that it is not restricted to the employment of the particular device described and illustrated therein. In its broad aspect my invention comprises a baille or its equivalent in the gas collecting device of a fused salt electrolysis cell, providing a separate chamber for the release of gasesliberated in the cell and a separate chamber for recirculation of the electrolyte when freed from said gases.

I claim:

1. In an electrolytic cell adapted to produce a gaseous product by electrolysis of a fused salt, a gas collecting dome partially submerged in the fused salt electrolyte and arranged above the zone of gas evolution so 'as to collect gas and fused salts rising therefrom, having a gas outlet in its non-submerged part, a partition in its submerged part forming a pair of adjacent chambers open into said non-submerged part, one chamber of said pair of chambers being open towards said zone of gas evolution and means to allow the rising fused salt to overflow into the other chamber of said pair, said other chamber being substantially closed from said gas evolving zone; and means for recirculating the fused salts from said other chamber back into the electrolyte in said cell.

2. In an electrolytic cell adapted to produce a gaseous product by electrolysis of afused salt, a gas collecting dome partially submerged in the fused salt electrolyte and arranged above the zone of gas evolution so as to collect gas and fused salt rising therefrom, having a gas outlet in its non-submerged part, a partition in its submerged part forminga pair of adjacent chambers open into the said non-submerged part, one chamber of said pair of chambers being open towards said zone of gas evolution, said partition" having perforations in its upper part to allow the rising fused bath to overflow into the other chamber of said pair, said other chamber being substantially closed from said gas evolving zone; and means for recirculating the fused salt from said other chamber back into the electrolyte in said cell.

3. In an electrolytic cell adapted to produce a gaseous product by electrolysis of a fused salt, a gas collecting dome partially submerged in the fused salt electrolyte and arranged above the zone of gas evolution so as to collect gas and fused salt rising therefrom, having a gas outlet in its non-submerged part, a partition in its submerged part forming a pair of adjacent chambers open into said non-submerged part, one chamber of said pair of chambers being open towards said zone of gas evolution, said partition having perforations in its upper part extending approximately from its upper margin down to the level of lowest average fused salt level in said cell outside of the gas collecting dome adapted to allow the rising fused bath to overflow into the other chamber of said pair, said other chamber being substantially closed from said gas evolving zone; and means for recirculating the fused salt from said other chamber back into the electrolyte in said cell.

4. In an electrolytic cell adapted to produce a gaseous product by electrolysis of a fused salt,

a gas collecting dome partially submerged in the fused salt bath and arranged above the zone of gas evolution so as to collect gas and fused salt rising therefrom, having a gas outlet in its nonsubmerged part, a partition in its submerged part forming a pair of adjacent chambers open into said non-submergedpart, one chamber of said pair of chambers being open towards said zone of gas evolution, the opening towards the non-submerged part of said dome being substantially smaller than the opening at the bottom, and means to allow the rising fused electrolyte to overflow into the other chamber of said pair, said other chamber being substantially closed from said gas evolving zone; and means for recirculating the fused salt from said other chamber back into the electrolyte in said cell.

5. In an electrolytic cell-adapted to produce a gaseous product by electrolysis of a fused salt, a gas collecting device partially submerged in the fused salt bath and arranged above the zone of gas evolution so as to collect gas and fused salt rising therefrom, having a gas outlet in its nonsubmerged part, an inclined bailie in its submerged part forming two adjacent chambers. open towards said non-submerged part, one of said chambers being open towards said zone of gas evolution, said inclined baffle having perforations in its upper part extending approximately from its upper margin down to the level of the lowest average level of the fused salt electrolyte in said cell outside of the gas collecting device, said upper margin being above the highest level of the fused salt occurring. in the gas collecting device, saidperforations adapted to allow the rising fused salt ,to overflow into the other chamber, said other chamber being substantially separated from said gas evolving zone by the said baffle and means to recirculate the fused salts from said other chamber back into the electrolyte in said cell. l

6. In an electrolytic cell adapted to produce a gaseous product by electrolysis of a fused salt, a gas collecting dome partially submerged in the fused salt bath and arranged above the zone of gas evolution so as to collect gas and fused salt rising therefrom, having a gas outlet in its nonsubmerged part, a partition in its submergedpart forming a pair of adjacent chambers open into said non-submerged part, one of the chambers of said pair being open towards said zone of gas evolution and means to allow the rising fused bath to overflow into the other chamber of said pair, said other chamber being substantially closed from said gas'evolving zone; means for recirculating the fused salt from said second chamber back into the electrolyte in said cell and means for keeping constant the level of the fused salt in said second chamber.

7. In an electrolytic cell adapted to produce a gaseous product by electrolysis of a fused salt, a gas collecting device partially submerged in the fused salt bath and arranged above the zone of gas evolution so as to collect gas and fused salt rising therefrom, having a gas outlet in its nonsubmerged part, an inclined battle in its submerged part forming two adjacent chambers open towards said non-submerged part, one of said chambers being open towards said zone of gas evolution, said inclined baflie having perforations in its upper part extending approximately from its upper margin down to the level of the lowest average level of the fused salt in said cell outside of the gas collecting device, said upper margin being above the highest level of the fused salt occurring in the gas collecting device, said perforations adapted to allow the rising fused salt to overflow into the other chamber, said other chamber being substantially separated from said gas evolving zone by said ballle and means to recirculate the fused salts from said other chamber back into the electrolyte in said cell and means for keeping constant the level of the fused salt bath in said other chamber.

8. In a fused salt electrolysis cell, a gas collecting device which comprises a gas collecting hood bmerged in the electrolyte and adapted to col ect gas arising from an, electrode, a gas collecting dome partially submerged in the electrolyte surmounting said hood, gas outlet means connected to said dome, a partition being disposed within said dome extending from one side of the dome at a point below the lowest level of the electrolyte-occurring in the dome to the other side of the dome at a point above the highest level occurring in the dome and forming two adjacent chambers, one of which is open towards the gas evolving zone of the electrolysis cell and towards the upper part of the dome, said partition having perforations in its upper part extending approximately from its upper margin 4 down to the level of the lowest average fused salt level in said cell, so as to allow the rising fused bath to overflow into the other chamber, said other chamber being substantially separated from said gas evolving zone, and means for recirculating the fused salts from said other chamber back into the electrolyte into a part of said cell which is not subjected to the action of electric current.

9. In a fused salt electrolysis cell, a gas collecting device which comprises a gas collecting hood submerged in the electrolyte and adapted to collect gas arising from an electrode, a gas collecting dome being partially submerged in the electrolyte surmounting said hood, gas outlet means connected to said dome, an inclined baiile disposed within said dome extending from one side of the dome at a point below the lowest level and towards upper part of the dome, said inclined baflle having perforations in its upper part extending approximately from its upper margin down to the level of the lowest average level of the fused salt in said cell outside of the dome, said upper margin being above the highest level of the fused salt occurring therein, said perforations adapted to allow the rising fused bathwhich is open towards the-gas evolving zone of to overflow into the other chamber, said other chamber being substantially separated from said gas evolving zone by said baflle, and means to re circulate the fused salts, from said second chamber back into the electrolyte in a part of the cell which is not subjected to the action of electric current.

10. In a fused salt-electrolysis cell, a gas collecting device which comprises a gas collecting hood submerged in the electrolyte and adapted to collect gas arising from an electrode, a gas collecting domepartially submerged in the electrolytesurmounting said hood, gas outlet means connected to said dome an inclined baflle being disposed within said dome extending from one side of the dome at a point below the lowest level of the electrolyte occurring in the dome to the other side of the dome at a point above the highest level occurring in the gas collecting device and forming two adjacent chambers. one of the electrolysis cell and towards upper part of the dome, said inclined baflie having perforations in its upper part extending approximately from its upper margin down to the level of the lowst average level of the fused salt bath in said cell outside of the gas collecting device, said upper margin being above the highest level of the fused salts'occurring in said dome, said perforations adapted to allow the rising fused bath to overflow into the other chamber, said other chamber being substantially separated from the said gas evolving zone'by said baflie and means to recirculate the fused salts from said other chamber back into the electrolyte'into a part of said cell which is not subjected to the action of electric current, and means for keeping constant the level of the fused salt'bath in said other chamber.

ERNEST R. CORNEIL. 2o 

